German Patent DE 197 19 066 C1 discloses a pipe coupling which comprises a sealing sleeve which accommodates a seal and is arranged inside a supporting body, the supporting body, at least adjacent to one side of the sealing sleeve, supporting locking elements for one end of an inserted pipe, and these locking elements can dig into the inserted pipe while being raised in the radial direction when extension stress occurs. The locking elements are rectangular clamping plates, which are supported on the supporting body and are preloaded in the extension direction of the pipe via springs supported on the supporting body. Here, the clamping plates are accommodated by the supporting body in such a way that they can be pushed out, the supporting body being formed in its center part from axially extending lugs. This construction is relatively complicated with regard to the number of components and the preassembly as well as the final assembly when coupling pipes.
Furthermore, German Patent DE 44 28 570 C1 discloses a pipe coupling in which a relatively complicated connecting socket is provided, which is to be made as a cast part, has inner grooves, requiring internal machining, for accommodating sealing collars and is provided with through holes transversely to the longitudinal axis, the through holes serving to accommodate clamping units. The latter may consist of a clamping screw and two locking elements which can be adjusted with the clamping screw and are in the form of clamping wedges or sleeves which have cutting ribs and can be restrained against the pushed-in pipe via the clamping screw. However, the clamping units, if they were to be preassembled, would be displaceable in the through holes and could then hinder the insertion of the pipe. In this respect, this pipe coupling is also complicated and difficult to assemble.